America’s Busiest Locks Handle 10,000 Ships Yearly with Just Gravity & 19th-Century Engineering

Soo Locks (Michigan)

Lake Superior sits 21 feet higher than the other Great Lakes, which used to be a problem if you wanted to float a thousand tons of iron ore to market. The solution, built in 1855, was elegantly simple: dig a canal, build some locks, let gravity do the work. Here’s the story and how to see this marvel up close.

When Native Americans Navigated the Rapids

Local Ojibway tribes, also known as Chippewa, named the rushing waters “Bawating,” meaning “the rapids.” For centuries, native peoples used this area as a key trading spot.

Native Americans carried their canoes around the dangerous rapids. This practice involved moving boats and goods overland to avoid water obstacles.

In 1797, the Northwest Fur Company built the first lock—a small 38-foot channel made just for “bateaux,” flat-bottomed boats used in the fur trade. 

Americans destroyed this Canadian-side lock during the War of 1812, forcing a return to the hard work of carrying goods through town.

How Congress Nearly Rejected the Canal

Michigan lawmakers pushed the federal government for years to support building a canal and locks. Many fought against the idea.

Southern Senator Henry Clay spoke out against the project, saying that building locks in the far-off Upper Peninsula would be like placing a canal “on the moon.” 

Most people saw Michigan’s northern peninsula as an empty wilderness with little value.

This view shifted dramatically when miners found rich copper and iron ore in the Upper Peninsula during the mid-1840s. These valuable minerals needed to reach factories in Cleveland and Detroit.

In August 1852, Congress granted Michigan 750,000 acres of public land to pay for canal construction, seeing the economic benefits of improving this key shipping route.

The Challenging Construction of the State Lock

Work crews began digging during summer 1853, facing tough challenges. Nearly 1,700 men worked at the project’s peak, earning just $20 monthly for hard 12-hour workdays.

Winter made their work even harder. Men often started their mornings hunting for tools buried by heavy overnight snowfalls.

A deadly cholera outbreak swept through the workforce, killing many men where they stood. Cholera, a disease causing severe diarrhea and dehydration, spread quickly in the crowded work camps. Despite these hardships, workers kept cutting the canal through solid rock.

The First Vessel Through the Completed Locks

Workers finished the State Lock in May 1855 after nearly two years of backbreaking work. On June 18, 1855, the steamer Illinois made history as the first vessel to pass through the new locks.

The trip past the rapids took less than an hour—a huge improvement over the days needed for portaging. The original State Lock had two connected chambers, each 350 feet long and 70 feet wide.

Each chamber lifted ships 9 feet, together handling the full 21-foot difference between lake levels. The locks linked to a one-mile canal that bypassed the dangerous rapids entirely, opening Lake Superior to more ship traffic.

How Iron Ore Transformed the Locks

During the first summer of use in 1855, ships moved just 1,500 tons of iron ore through the locks. Within five years, this amount jumped to 120,000 tons as mining spread across the Upper Peninsula.

The Civil War created huge demand for iron ore to make weapons and military gear. The locks proved vital to the Union’s war effort by helping move raw materials to steel mills.

By 1883, traffic through the canal reached 4,000 vessels carrying 1.8 million tons of freight. Ten years later, volume soared to 12,000 ships moving over 10 million tons through the Weitzel Lock alone.

When the Federal Government Took Control

As shipping traffic grew, Michigan struggled to maintain and expand the busy waterway. In 1870, Congress set aside $150,000 for improvements to the St. Marys Falls Canal, seeing its national importance.

The state handed control of the locks to the federal government in 1881. Under federal management, the toll system ended. Before this, ships paid four cents per ton to use the locks, later lowered to three cents.

The Army Corps of Engineers built the Weitzel Lock, measuring 515 feet long, 80 feet wide, and 17 feet deep with a 20-foot lift capacity. Unlike the original State Lock, this new passage needed only a single chamber to raise or lower vessels the full distance between lake levels.

How the Locks Work Using Only Gravity

The Soo Locks work using gravity and water pressure, with no mechanical pumps. This clever design works through gates and valves that control water flow.

When a ship enters a lock chamber, huge gates close behind it. If the vessel needs to go up, valves open to let water flow in from the higher level. For going down, valves release water to the lower level. The Poe Lock uses 22 million gallons of water for each complete cycle.

The whole process takes about 21-22 minutes for the biggest ships. Today, only 4% of the St. Marys River’s natural flow goes through the rapids. The rest flows through power canals (95%) or runs the locks themselves (1%).

The Poe Lock Revolution for Larger Ships

The original Poe Lock, finished in 1896, marked a major step forward in shipping infrastructure. Built by Orlando Poe, who earlier planned the burning of Atlanta during the Civil War, it ranked as the world’s largest lock at 800 feet long and 100 feet wide.

As Great Lakes ships grew ever larger, the Poe Lock underwent a complete rebuild. The new lock opened in 1969, with the Phillip R. Clarke becoming the first vessel to pass through the expanded chamber.

Today’s Poe Lock handles massive lake freighters, including the Paul R. Tregurtha, the largest vessel on the Great Lakes at 1,013.5 feet long and 105 feet wide.

The Economic Lifeline of the Great Lakes

The Soo Locks move nearly 86 million tons of cargo yearly, serving as the key link in the Great Lakes shipping network. Through these locks passes 95% of the United States’ iron ore, the raw material needed for domestic steel production.

The Department of Homeland Security has studied what would happen if the Poe Lock failed. They found that a six-month unplanned closure would increase the U.S. unemployment rate by 5.8 percentage points, possibly triggering a recession.

Visiting the Soo Locks

The Soo Locks Visitor Center welcomes about 500,000 tourists yearly between May 1 and October 31.

You’ll be able to see the fascinating process of raising and lowering vessels. Engineers Day, held on the last Friday of June, offers a rare chance to walk across the actual lock gates and get an up-close view of the machinery normally off-limits to the public.

The site includes the historic 1899 U.S. Weather Bureau Building, now housing the Great Lakes Shipwreck Historical Society with displays about the region’s maritime heritage.

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